Fortunately, Python developers can now choose from four dedicated IDEs, all with their strong points: IDLE, Wing IDE, PythonWorks, and Pythonwin:
IDLE is the only cross-platform IDE. It uses tkInter and comes with every standard Python installation.
Wing IDE, made by Archeopteryx, is Linux-only, and uses the PyGTK GUI bindings. Wing IDE has only just been released.
PythonWorks, by PythonWare, is currently Windows-only. Like IDLE, it is based on tkInter (although you wouldn't think so, looking at it), and like Wing IDE, is a commercial package. PythonWorks is relatively new, too, and a Linux version was promised before the end of 2000.
Pythonwin is, as its name implies, for Windows only. If you build using the Python bindings to MFC, it will integrate seamlessly into the environment. Pythonwin is free software.
Of course, there are other possibilities. I've already mentioned Emacs, which has a nice Python mode that includes a class browser, but there's also Red Hat's Source Navigator, an IDE that includes Python support in its latest release. Another option is Visual SlickEdit, which also offers some measure of Python support. Still, these additional choices are more like editors than IDEs, and they are not Python specific.
A very recent addition to the cast that is worthy of a brief note is eric, Phil Thompson's PyQt debugger and class browser. It is cross-platform between Unix/X11 and Windows and shows a lot of promise.